The present invention relates to battery powered forklift trucks, and in particular, to an electric reach truck having a pivotal control panel.
Forklift trucks are typically diesel powered or battery powered. The present invention relates to battery powered trucks and addresses the technical problem of improving the access to the battery in such a forklift truck. The invention is particularly relevant to reach trucks which are typically used within warehouses and in other confined spaces and are required to be compact in design. However, the invention may also be applied to other types of forklift trucks.
The battery used to power an electric reach truck is a large and heavy lead acid battery which, as well as providing power to a drive motor and to at least one motor which drives the pump or pumps for the working and steering hydraulics, acts as a counter-weight for the load being lifted or moved on the forks.
Access is required to the battery in order to provide for charging, topping up and specific gravity checks, as well as general inspection and equalizing charges. All of these maintenance requirements are well-known in the art and will not be described in detail in this specification. In certain applications for forklift trucks, it is normal to replace the battery up to three times per day in order to allow continuous service of the truck. Therefore, the ease of access for removing and replacing the battery will considerably enhance the operating efficiency of the truck. Since the cost of a battery represents between 10 and 15% of the cost of the truck, battery maintenance cannot be neglected.
An electric reach truck has to be of compact design, yet provide the driver with good visibility so that he can at all times see as far as possible the location of the forks. The battery compartment must be located as low as possible in the vehicle in order to keep a low center of gravity for stability. For a reach truck, a number of operating controls are necessary in order to control the lift, reach, tilt and side shift of the forks. An auxiliary horn and emergency stop control as well as other indicators to show, for example, working time or the state of the battery charge are also typically required in a control panel.
In existing electric reach trucks, two systems have been provided for battery access. In one arrangement, as employed in many electric reach trucks manufactured by, for example, Boss (WR series), Linde Lansing, Still and Saxby (464 range), the battery unit is mechanically latched to the reach carriage so that the complete assembly may be reached towards the mast using the battery's own power under the control of the hydraulic system. This configuration requires that the battery be located between the operator and mast, requiring the operator to look sideways over the battery and control panel to see the forks. The control panel is typically located in a fixed housing that overlies the battery. The linkages needed to latch the battery to the reach carriage are also complex, expensive and prone to failure. A further disadvantage of this system is that battery access is extremely difficult in the event of battery failure.
An alternative arrangement is to mount the battery on rollers and to provide a separate frame which can be located adjacent to the battery to enable an operator to roll the battery out of the truck manually. This is usually the less favored option though manufacturers are prepared to offer it at an extra cost. Servicing of the battery without removing the battery is generally not possible. In either case, when the battery has to be removed it is necessary to either use a crane (once the battery has been reached out from beneath the control panel housing) or transfer the battery from its carriage sideways using rollers.
In another design of electric forklift truck, known generally as a counterbalance truck, the battery is located to the rear of the vehicle instead of beneath the control panel housing. This configuration is adopted in the Still R50 range, and although providing for good driver visibility in allowing the controls to be mounted at a lower level, this arrangement is at the expense of overall compactness of design.
Another technical problem associated with the design of electric forklift trucks is separating the hydraulic systems and the electrical systems, in order to minimize the risk of contamination of the electrical components by hydraulic fluid.
In most existing forklift trucks, the operator controls for the working hydraulics are themselves hydraulically operated levers. This gives rise to problems of shock loading. Because the movement of the levers directly governs the movement of a valve spool, sudden and vigorous movement of the levers will result in hydraulic shock which can effect the whole hydraulic system. Abuse of this nature can result in early fatigue failure problems with the mechanical components because they are continually subjected to such shocks. In existing truck designs, attempts have been made to solve this technical problem by inserting accumulators to minimize the shock. However, this requires an extra component in the hydraulic circuit and results in increased expense and further maintenance and reliability problems. However, Mitsubishi in their diesel powered forklift truck have utilized miniature joysticks which provide an electrical position output in order to control the working hydraulics.
Accordingly, there is a need for a forklift truck which provides easy access to the battery and solves the problem of hydraulic shock by pre-processing the electrical signals generated by control elements such as joystick controls before they are used to control movement of the hydraulic valves.